1. Field of the Invention
The present invention relates to an inner cutter for a reciprocating type electric shaver in which a plurality of arch-shaped cutter blades are integrally formed, and these cutter blades make sliding contact with the inside surface of an arch-shaped outer cutter while making reciprocating motion.
2. Description of the Related Art
In a reciprocating type electric shaver, an inner cutter, while making reciprocating motion, makes sliding contact with the inside surface of an arch-shaped outer cutter and cuts whiskers (hair) that enter the openings formed in the outer and inner cutters; and there are typically two types of inner cutters. One is an assembled-type inner cutter, and the other is an integral-type inner cutter, as disclosed in Japanese Patent Application Laid-Open (Kokai) No. S62-148684.
In the assembled-type inner cutter, a plurality of semicircular cutter blades are punched out of a thin sheet, and these semicircular cutter blades are aligned at fixed intervals and supported in a supporting stand. In this inner cutter, a plurality of cutter blades are prepared separately from one another, and the centers and both end portions of these cutter blades are attached to and supported by a support member. Accordingly, the problem with this assembled-type inner cutter is that assembly is troublesome, it takes many manufacturing steps, and the productivity is low.
On the other hand, in the integral-type inner cutter, all the cutter blades are integrated. In one of the integral-type inner cutter, for example, slits (grooves) are formed in a transverse direction in a tubular base material, so that the arch-shaped portions remained between the slits becomes the cutter blades. It is also possible to bend a thin sheet of metal or ceramic or the like in a substantially arch shape and form slits by cutting along the ridge line, thus forming arch-shaped cutter blades that are parallel and at a fixed interval.
In another integral-type inner cutter, the inner cutter is integrally formed of a soft material such as plastic or the like, and a coating layer of chromium or the like is formed on its entire surface, and then its sliding surface with the inside surface of the outer cutter is polished, as disclosed in Japanese Patent Application Laid-Open (Kokai) No. S62-148684.
Meanwhile, when an electric shaver is used, vibration and sound are generated by the internal electric motor and drive mechanism, and sound (cutting sound, shaving sound, friction sound) also occurs due to the blade vibration when cutting hair that has entered the openings of the outer and inner cutters and due to the vibration caused by friction between the outer cutter and the inner cutter. The hair cutting sound and friction sound due to the outer cutter and the inner cutter in particular are likely to be sensed by the user because the outer cutter makes direct contact with the skin. Accordingly, they directly affect how good or bad the use feeling of the shaver is.
In view of the issues above, in one of the proposed inner cutters, a plurality of projecting strips, that intersect the inner cutter sliding direction, are formed in a single flat metal sheet, this metal sheet is bent in the direction orthogonal to the sliding direction to make an arch shape, and then the outer peripheral surface is polished to separate the cutter blades (Japanese Patent Application Laid-Open (Kokai) No. H10-323461). In other words, in this inner cutter, projecting strips are provided in a flat metal sheet by forming a plurality of cut grooves by pressing or by using a grinding wheel, and these projecting strips are separated by polishing the outer periphery, thus making an arch-shaped cutter blade and thereby enhancing the cutting sound when in use.
In the assembled-type inner cutter disclosed in this Japanese Patent Application Laid-Open (Kokai) No. H10-323461, since the center part of the cutter blade is supported by an inner cutter stand, the cutter blade (inner cutter sheet (15)) is not very flexible, and cutting sound is difficult to generate (as described in paragraph 0022 of this prior art). This prior art, Japanese Patent Application Laid-Open (Kokai) No. H10-323461, further describes that cut-outs ((71) in FIG. 9) are provided at the inner peripheral edge of the cutter blade so as to increase the arch-bending workability and to improve the fit with the outer cutter, thus improving the cutting feeling (see paragraph 0082 of this prior art).
However, in the inner cutter of this Japanese Patent Application Laid-Open (Kokai) No. H10-323461, the vibration characteristics and intrinsic vibration frequency of the cutter blades are determined, for instance, by the thickness of the flat sheet that is used, by the height of the projecting strips (width of the cutter blade in the radial direction), and by the thickness of the projecting strips (thickness of the cutter blade in the inner cutter reciprocating direction). Therefore, even if the cutting sound can be made loud by changing these parameters, it is difficult to provide suitable sound quality.
Accordingly, a concept that has been considered is to make the cutter blades vibrate easily in the inner cutter reciprocating direction and actively generate an excellent sound. The applicant of the present application has proposed, in Japanese Patent Application No. 2004-042658, to form a vibration control part for allowing vibration of the cutter blades near the connecting portion that connects both end portions of an arch-shaped cutter blade to the side edge part.
However, when vibration of the cutter blades are actively utilized in this manner to improve the sound quality, stress concentrates at the connecting portion between both end portions of the cutter blades and the side edge part, and a problem of low durability was found. An opposite strategy was thus considered—improving durability by shortening the cutter blades and making vibration difficult —, but in this case the problem of low sound quality occurred.